排序

在给定f[i][j] 数组中 在图论思想上 我们定义f[i][j]表示从i到j的路径存在与否 因为涉及多点多次的关系转移
我们通过floyd来进行两个点的连通情况更新

代码

#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

const int N = 26;

int n, m;
bool g[N][N], d[N][N];
bool st[N];

void floyd()
{
    memcpy(d, g, sizeof d);

    for (int k = 0; k < n; k ++ )
        for (int i = 0; i < n; i ++ )
            for (int j = 0; j < n; j ++ )
                d[i][j] |= d[i][k] && d[k][j];
}

int check()
{
    for (int i = 0; i < n; i ++ )
        if (d[i][i])
            return 2;

    for (int i = 0; i < n; i ++ )
        for (int j = 0; j < i; j ++ )
            if (!d[i][j] && !d[j][i])
                return 0;

    return 1;
}

char get_min()
{
    for (int i = 0; i < n; i ++ )
        if (!st[i])
        {
            bool flag = true;
            for (int j = 0; j < n; j ++ )
                if (!st[j] && d[j][i])
                {
                    flag = false;
                    break;
                }
            if (flag)
            {
                st[i] = true;
                return 'A' + i;
            }
        }
}

int main()
{
    while (cin >> n >> m, n || m)
    {
        memset(g, 0, sizeof g);
        int type = 0, t;
        for (int i = 1; i <= m; i ++ )
        {
            char str[5];
            cin >> str;
            int a = str[0] - 'A', b = str[2] - 'A';

            if (!type)
            {
                g[a][b] = 1;
                floyd();
                type = check();
                if (type) t = i;
            }
        }

        if (!type) puts("Sorted sequence cannot be determined.");
        else if (type == 2) printf("Inconsistency found after %d relations.\n", t);
        else
        {
            memset(st, 0, sizeof st);
            printf("Sorted sequence determined after %d relations: ", t);
            for (int i = 0; i < n; i ++ ) printf("%c", get_min());
            printf(".\n");
        }
    }

    return 0;
}